Ich-1 is a human cysteine protease that is a member of a family of cysteine proteases including interleukin-1.beta. converting enzyme (ICE), a protein essential for the maturational processing of interleukin-1.beta. (see e.g., Black, R. A., et al. (1988) J. Biol. Chem. 263:9437-9442; Kostura, M. J., et al. (1989) Proc. Natl. Acad. Sci. USA 86:5227-5231; Thornberry, N. A., et al. (1992) Nature 356:768-774; Ceretti, D. P., et al. (1992) Science 256:97-100) and the Caenorhabditis elegans protein Ced-3, a protein required for apoptosis during the development of C. elegans (see e.g., Yuan, J., et al. (1993) Cell 75:641-652). Other members of this family include CPP32/Yama (Fernandes-Alnemri, T., et al. (1994) J. Biol. Chem. 269:30761-30764; Tewari, M., et al. (1995) Cell 81:801-809), SCA (Wang, X., et al. (1995) J. Biol Chem. 270:18044-18050), Ich-2/ICE.sub.rel II/Tx (Kamens, J., et al. (1995) J. Biol Chem. 270:15250-15256; Munday, N. A., et al. (1995) J. Biol. Chem. 270:15870-15876; Faucheu, C., et al. (1995) EMBO J. 14:1914-1922), ICE.sub.rel III/Ty (Munday, N. A., et al. (1995) J. Biol. Chem. 270:15870-15876; Faucheau, C., et al. (1996) Eur. J. Biochem. 236:297-313), Mch2 (Fernandes-Alnemri, T., et al. (1995) Cancer Res. 55:2737-2742) and Mch3/ICE-LAP3/CMH-1 (Fernandes-Alnemri, T., et al. (1995) Cancer Res. 55:6045-6052; Duan, H., et al. (1996) J. Biol. Chem. 271:1621-1625; Lippke, J. A., et al. (1996) J. Biol. Chem. 271:1825-1828). The cDNA for Ich-1 has been isolated and the predicted amino acid sequence of Ich-1 displays approximately 30% amino acid identity to ICE (Wang, L. et al. (1994) Cell 78:739-750). The mouse homolog of Ich-1, termed Nedd2, also has been identified and similarly exhibits approximately 30% amino acid identity to ICE (Kumar, S., et al. (1994) Genes Dev. 8:1613-1626).
Members of the ICE-related family of proteins are involved in cytokine maturation leading to inflammation and in apoptosis. In particular, Ich-1 has been implicated in apoptosis and neuronal development. For example, Ich-1 (and its murine homolog Nedd2) induces apoptosis when overexpressed in mammalian cells (Kumar (1994) supra; Wang (1994) supra). Additionally, the Nedd2 gene was identified based upon its developmentally down-regulated expression in the adult brain (Kumar, S. et al. (1992) Biochem. Biophys. Res. Commun. 185:1155-1161). During murine embryonic development, the Nedd2 gene is ]highly expressed in several tissues undergoing a high rate of apoptosis, including the central nervous system (Kumar (1994) supra).
In vitro studies have demonstrated that ICE cleaves prointerleukin-1.beta. at Asp.sub.116 -Ala.sub.117 to release the fully active 17 kDa form (Black (1988) supra; Kostura (1989) supra). ICE also cleaves prointerleukin-1.beta. at Asp.sub.27 -Ala.sub.28 to release a 28 kDa form. Cleavage at these sites is dependent upon the presence of aspartic acid in the P1 position (the position immediately amino-terminal to the cleavage site) (Kostura (1989) supra, Howard, A., et al. (1991) J. Immunol. 147:2964-2969; Griffin, P. R., et al. (1991) Int. J. Mass. Spectrom. Ion. Phys. 111:131-149). However, an aspartic acid in the P1 position is not sufficient for ICE specificity. For example, several other proteins containing Asp-X bonds, including prointerleukin-1.alpha., are not cleaved by ICE (Howard (1991) supra). An optimal minimal substrate for ICE has been identified as containing the tetrapeptide Tyr-Val-Ala-Asp (SEQ ID NO: 44) (Thornberry (1992) supra).